In such an arrangement known from DE-PS 591 625, in the stationary condition an anode part is brought into good thermally conducting contact with a heat-dissipating body.
When the X-ray tube is switched on, the striking electron beam produces in the rotary anode stem tube a high heat dissipation, which can lead there to a temperature of, for example 1500.degree. C. Before the tube is switched on again, a cooling to, for example, 150.degree. C. must take place in order that, when the tube is subsequently switched on again, the occurrence of too high temperatures is avoided.
It is attempted to keep the required cooling time (in dependence upon the application, for example, approximately 20 minutes) as short as possible. At high temperature, the dissipated heat is conducted away from the anode stem tube mainly by radiation. At low temperatures, on the contrary, essentially only the heat transport through the material of the rotary anode and via the bearing to a bearing support dissipating heat to the environment is left. More particularly with the use of sliding bearings, this path can contribute essentially to shortening of the required cooling time of the rotary anode stem tube.
A substantial reduction of the heat resistance of the heat dissipation path, though permanent or, above known case described in the only in the stationary condition, can lead to unacceptable high bearing temperatures, however.